1. Field of the Invention
The present invention relates to a mobile communication system which carries out information transmission between vehicles traveling on a road, or between vehicles and a roadside communication network, and particularly to a mobile communication system capable of offering sophisticated services applicable in common to expressways or the like in future.
2. Description of the Background Art
The Road/Automobile Communication System, which is administered by the Public Works Research Institute of the Ministry of Construction of Japan, is known as one of the conventional mobile communication systems which provide channels between vehicles and a roadside communication network. Such a system is provided with a plurality of on-road stations installed at intervals for projecting spotlight-like beacons onto a road like a street or expressway, to carry out intermittent communications between the mobile station of a vehicle and the roadside communication network when the vehicle passes through a small zone (radio zone) intermittently formed on the road.
Thus, the vehicle obtains its own position information by the intermittent communications which are carried out at the radio zone interval between the mobile station and the on-road station that forms the spotlight-like radio zone and that receives radio waves from the mobile station. Accordingly, the position information obtained by the conventional system is rather inaccurate. As a result, the conventional system cannot offer intelligent information about driving if precise position information about vehicles is required. For example, it is impossible to carry out automatic driving in which the vehicles drive themselves automatically in response to their position information, or platooning driving in which a plurality of vehicles drive themselves in a group, because of the lack of precise position information for controlling the driving.
As another communication system, a method is proposed which provides an uninterrupted message channel between an automobile and a leakage coaxial cable laid along a roadside. Even in this case, a problem still remains in that the position information of the automobile cannot be obtained.